Inconsistent results for adding child node in a JTree

Question

I have a JTree where I add child nodes when a user clicks on the node or handle. When the user clicks on the node, through implementing TreeSelectionListener interface, I add a node, the tree expands, and I see the newly added node. However, when the user clicks on the handle, through implementing the TreeExpansionListener, the tree does not expand and I do not see the newly added node. The problem is repeatable by compiling the code below.
Why is there this difference? Aren't all the methods implemented through the TreeSelectionListener and TreeExpansionListener in the SWT thread?
public class TestFrame extends JFrame implements TreeSelectionListener, TreeExpansionListener {
     public TestFrame() {
          String[] alphabets = {
                    "a", "b", "c", "d", "e", "f", "g",
                    "h", "i", "j", "k", "l", "m", "n",
                    "o", "p", "q", "r", "s", "t", "u",
                    "v", "w", "x", "y", "z"
          DefaultMutableTreeNode top = new DefaultMutableTreeNode("CEDICT");
          for(int i=0; i < alphabets.length; i++) {
               DefaultMutableTreeNode node =
                    new DefaultMutableTreeNode(alphabets) {
                    public boolean isLeaf() { return false; }
               top.add(node);
          JTree tree = new JTree(top);
          tree.getSelectionModel().setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION);
          tree.addTreeSelectionListener(this);
          tree.addTreeExpansionListener(this);
          tree.setShowsRootHandles(true);
          JScrollPane treePane = new JScrollPane(tree);
          treePane.setHorizontalScrollBarPolicy(
                    JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
          treePane.setVerticalScrollBarPolicy(
                    JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
          treePane.setSize(new Dimension(200,400));
          treePane.setPreferredSize(new Dimension(200,400));
          getContentPane().setLayout(new BorderLayout());
          getContentPane().add(treePane, BorderLayout.CENTER);
          Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
          int inset = 50;
setBounds(inset, inset,
screenSize.width - inset*2,
screenSize.height - inset*2);
          setLocationRelativeTo(null);
          setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          pack();
          show();
     public static void main(String[] args) {
          SwingUtilities.invokeLater(new Runnable() {
               public void run() {
                    JFrame.setDefaultLookAndFeelDecorated(true);
                    TestFrame frame = new TestFrame();
     public void valueChanged(TreeSelectionEvent e) {
          JTree tree = (JTree)e.getSource();
          DefaultMutableTreeNode node =
               (DefaultMutableTreeNode) tree.getLastSelectedPathComponent();
          System.out.println(node);
          Date date = new Date();
          node.add(new DefaultMutableTreeNode(date.toString()));
     public void treeCollapsed(TreeExpansionEvent event) {
          JTree tree = (JTree)event.getSource();
          TreePath path = event.getPath();
          DefaultMutableTreeNode node =
               (DefaultMutableTreeNode) path.getLastPathComponent();
          System.out.println(node);
          Date date = new Date();
          node.add(new DefaultMutableTreeNode(date.toString()));
          tree.invalidate(); //does not help to show newly added child
     public void treeExpanded(TreeExpansionEvent event) {
          JTree tree = (JTree)event.getSource();
          TreePath path = event.getPath();
          DefaultMutableTreeNode node =
               (DefaultMutableTreeNode) path.getLastPathComponent();
          System.out.println(node);
          Date date = new Date();
          node.add(new DefaultMutableTreeNode(date.toString()));
          tree.invalidate(); //does not help to show newly added child

Answer 1

I couldn't figure out why inserting a node in the valueChanged(...) method works. In all three methods no listeners are notified about the change, so you would think all three would fail.
For a JTree using the DefaultTreeModel the nodesWereInserted(...) method needs to be called. For example, if I change your last three methods to this
public void valueChanged(TreeSelectionEvent e) {
   insertNode((JTree) e.getSource(),
              (MutableTreeNode) e.getPath().getLastPathComponent());
public void treeCollapsed(TreeExpansionEvent event) {
   insertNode((JTree) event.getSource(),
              (MutableTreeNode) event.getPath().getLastPathComponent());
public void treeExpanded(final TreeExpansionEvent event) {
   insertNode((JTree) event.getSource(),
              (MutableTreeNode) event.getPath().getLastPathComponent());
public void insertNode(JTree tree, MutableTreeNode parent) {
    Date date = new Date();
    MutableTreeNode child = new DefaultMutableTreeNode(date.toString());
    int index = parent.getChildCount();
    parent.insert(child,index);
    ((DefaultTreeModel) tree.getModel())
            .nodesWereInserted(parent,new int[]{index});
}then it works as you desire. You can (and should) of course use the DefaultTreeModel's own insert method.
DefaultTreeModel#insertNodeInto(MutableTreeNode,MutableTreeNode, int)